Arsenic is an element that is deadly to most living creatures, but bacteria living in California's Lake Mono thrive on it. Today NASA explains how those poison-eating organisms are changing the way we search for extraterrestrial life.

News of an arsenic-eating bacteria residing in alkaline Lake Mono first came two years ago. As reported by the BBC, researchers discovered a bacterium that utilizes arsenic in photosynthesis instead of water to transform carbon dioxide into food.

So what is different about NASA's new finding?

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Dr. Felisa Wolfe-Simon of the US Geological Survey in Menlo Park says that the microbe, known as GFAJ-1, isn't simply substituting arsenic for water. It's substituting arsenic for phosphorus, one of the fundamental building blocks of life.

"We know that some microbes can breathe arsenic, but what we've found is a microbe doing something new — building parts of itself out of arsenic," said Felisa Wolfe-Simon, a NASA Astrobiology Research Fellow in residence at the U.S. Geological Survey in Menlo Park, Calif., and the research team's lead scientist. "If something here on Earth can do something so unexpected, what else can life do that we haven't seen yet?"

During the press conference, Wolfe-Simon explained that the reason arsenic is so toxic to normal life, is that it's so close to phosphorus our bodies can't tell them apart.

"Nothing should have grown," she said of the environment of Lake Mono. Yet it did. "It has solved the challenge of being alive in a very different way than we knew of."

The arsenic is associated specifically with a band of genomic DNA. It's inside the cell. It's part of the microbe, taking the place of phosphorus.

Arizona State University's Dr. James Elser explained that the existence of an organism that does without phosphorus has far-reaching possibilities. "It's very exciting to think about the possibilities of a clever organism that's evolved beyond using phosphorus," said Elser after explaining how vital the element is to life on Earth. He marveled over the possible uses for such an organism, including water treatment, bio-energy production, and even recovering phosphorus used in other processes.

Dr. Steven Benner of the Foundation for Applied Molecular Evolution put things in layman's terms. Using a steel chain to represent a phosphorus bio-polymer, he likened arsenic to a tinfoil link. When a link is broken it searches for a replacement, and the chain could be confused by the similar structure of arsenic. He called the element a demon wolf, tricking organisms into taking it it.

"Remember, the weakness of the link is a weakness measured at room temperature...in water," Benner said. There are places in our own solar system where the conditions are very different that could support another sort of life entirely, as is the case with Lake Mono and GFAJ-1.

NASA astrobiologist Dr. Pamela Conrad spoke next. She develops habitability metrics for alien worlds, and she's delighted by the discovery, as it will make her change the way she defines those metrics. "The implication is that we still don't know everything there is to know about what might make a habitable environment on another planet. We have to increasingly broaden our perspective." Conrad said that while arsenic might not be a essential element life, it is a tolerable one, and that opens up the potential for other tolerable elements.

Dr. Felisa Wolfe-Simon closed the conference by saying this wasn't about arsenic and wasn't about Mono Lake. "It's about thinking about life in a planetary concept and asking questions - simple questions, with a simple experimental design."